Fundamentals of Interface and Colloid Science

Publisher Summary This chapter discusses Lyklema's definition of a colloid as “an entity, having at least in one direction a dimension between 1 nm and 1 μm—that is, between 10 –9 and 10 –6 m. The entities may be solid, liquid, or, in some cases, even gaseous. They are dispersed in the medium,” which may be also solid, liquid, or gaseous. All the colloids can be defined as “a collection of particles immersed in a liquid”; the particles can be solid (a suspension or dispersion), liquid (an emulsion), or gas (a foam). These three types of dispersed systems play an important role in all kinds of applications: paints, latices, food products, cements, minerals, ceramics, blood, and many others. All these disperse systems have one common feature; because of their small size, they all have a high surface area relative to their volume. It is the surface-related phenomena that primarily determines their behavior in various processes and justifies consideration of colloids as effectively a different state of matter. The chapter includes the combined terms and methods that have been created over the course of two centuries to characterize these very special systems. Real heterogeneous systems, by their very nature, are quite complex. Two of these complexities are the variation of the particle size and the shape within a particular dispersion. There are three groups of traditional particle sizing methods that can be applied to characterize the size of colloidal particles. These groups are: (1) counters, (2) fractionation techniques, and (3) macroscopic fitting techniques.